Variable frequency apparatus



Dec. 22, 1942. N. E. LINDENBLAD l 2,305,882

VARIABLE FREQUENCY APPARATUS Filed April 8, 1941 FREQUENCY AAM/L 45 asc. 43

FREQUENCY A//LS E. LINDENBLAD BY Mgg/wm ATfoRNEY Patented Dec. 22 1942 UNITED STATES PATENT OFFICE l l. Fazisr ArrARA'rUsl l l to Radio Corporation of America, a

of Delaware corporation 4 Application Apru s, 1941, semi No. 387,376

' s claims. .(cl. 17o-111.5) t

My present invention relates to variable frequency circuits, apparatus andsystems, and is a continuation-impart of my copending application Serial No. 226,674, filed August' 25, 1938, now Unitid States Patent No. 2,245,597, 'grantedJune 17, 1 4i.

Referring to the drawing,` there is shown a concentric resonant line lwhose inner conductor One object of my invention is to'provide an;

improved variable frequency oscillation generator which may be used for the transmission of frequency, phase, or more generally, angular velocity modulated waves. As will be explained more fully hereinafter, my invention is not limited to the transmission of wavesbut may also be employed wherever a variable frequency gen erator of controllable frequency may \be desired, as, for example, in a radio receiver of the superheterodyne type employing an auto atic'requency controlled local oscillator. "16 Other objects as well as features and. adyantages of my invention will appear as thev more detailed description thereof proceeds.

The output of the generator will be a phase -modulated wave if the modulating or speech' input Waves are amplified in direct proportion to modulation frequency prior to use for varying the frequency of the oscillator. To this end, namely, phase modulationL I prefer to employ the pre-emphasizing circuits shown, and described in Peterson Patent No. 2,070,681.

Other pre-emphasizing circuits, such as described in Hansell Patent No. 2,179,182 and Bown Patent No. 2,212,338, for the modulating waves may also be'employed with my system. When this is done, proper corrections should be introduced at the receiver as described in the Hansell and Bown patents and also as described in Crosby Patent No. 2,230,212.

When using my variable frequency generator as a local, automatically controlledgenerator in a superheterodyne-receiver, it will occupy the position of vthe local oscillator 33 of Fig. 4 of Seeley Patent No. 2,121,103. The automatic frequency control voltages derived from the dis-y y criminator-detector 'circuits of the Seeley vpatent are impressed across the terminals of the secondary of'the modulation transformer,-which transformer, in the case of a receiver, is, of'

course, omitted. l

The present invention provides a push-pull frequency modulator circuit (broadly known by the term angular velocity modulator) asso-A Y elated with a concentric line'resonator of the type to which a multiplicity of voltage connections can be made without disturbing its balance or introdpcing multiple degrees of freedom.

is composed-of two coaxial rods or tubes 2, 2 conductively coupled to `opposite end plates 3 and t, and capacitively coupled together at their adjacent ends by means of plates 4, 4. Interposed between the plates 4, d are metal plates or discs 8 and 9 suitably spaced apart andinsulatingly mounted in a manner not shown. Discs 8 and 9 are wider than plates if, li to enable a short and low reactance connection of minimum length to be made between the discs and the associated vacuum tube electrodes. -The outer conductor 2tl is Aenlarged at its center portion to yaccommodate the wide plates t and 9 for completelyfshielding the same.

The voltage distribution ofthe concentric line is such that the rods 2, 2 have opposite instantaneous polarities relative to each other, and a space of zero voltage exists between plates 8 and 2. are also at opposite instantaneous polarities relative to each other. The markings minus and plus indicate the instantaneous relative polarities at a given moment. During another portion of the cycle, the polarities on these plates will, of course,I be reversed.

In the system of the drawing, a master oscillator comprising a pair of push-pull vacuum tubes 43, M drives aradio frequency push-pull neutralized amplifier comprising a pair of vacuum tubes t5, d6. Output energy from the amplifier is derived from tuned circuit 41. For modulating the output there is provided a pair of modulating tubes t8, 49. By throwing the switch 50 to the left, the output energy can be amplitude modulated, while frequency modulation can be oby tained by throwing this switch to the right.

modulator.

When amplitude modulation is desired, only the oscillator and the radio frequency amplifier are energized. The radio frequency amplifier is then modulated. When frequency modulation is desired, the feed-back or frequency modulator is' also energized. The modulator is then connected to modulate the feed-back of -the frequency The radio frequency amplifier is then not modulated but operates as a straight amplifier.

The frequency modulator operates as an aux- I iliary feedback circuit to the resonance line system. The feedback is controlled by the coupling through the coupling condensers 6 and 'l and by the amplitude of the plate voltage. Of these, the

coupling, after -the best adjustment has been 5 found, is left constant. The feedback is then con- It will thus be obvious that plates 8 and S trolled only by the variations in plate voltage caused by the modulator. A radio frequency ground is indicated in the forni of a condenser I2 at the mid point of the resistor I3. 'I'his condenser serves to prevent any unbalanced stray from entering the modulator.

The push-pull drop across the resistor I3 determines the variation of current going through the coupling condensers 6 and 1. A variation in this current will, of course, vary the frequency of the resonance line system.

What is claimed is:

1. The combination with an oscillation generator system comprising a pair of vacuum tube `oscillators having associated therewith a concentric resonant line oscillatory circuit for controlling the frequency thereof, of an angular velocity modulator in the form of a pair of electron discharge devices having their anodes capacitively coupled to different points on said resonant line oscillatory circuit which have opposite instantaneous polarities, and means for varying the conductivity of said pair of electron discharge devices in accordance with signal modulations.

2. The combination with an oscillation generator system comprising a pair of oscillators having associated therewith aV tuned high frequency circuit comprising concentric inner and outer conductors, said inner conductor comprising a pair of spaced rods arranged in the same straight line connection from the anode of said last device to the other rod of the inner conductor, a resistor connected between the anodes of said devices, a connection from the midpoint of said resistor to a signal modulator circuit, and means for grounding said midpoint from a radio frequency standpoint.

4. The combination with an oscillation generator system comprising a pair of oscillators having associated therewith a tuned high frequency circuit comprising concentric inner and outer conductors, said inner conductor comprising a pair of spaced rods having remote ends connected to said outer conductor, the adjacent ends of said rods being so spaced as to provide a capacitor, and a `pair of conducting plates placed between the adi a cathode, an anode and a control electrode, means and having remote ends connected to said outer conductor, the adjacent ends of said rods rbeing so spaced as to provide a capacitor, and a pair of parallel conducting plates placed between the adjacent ends of said rods with their planes transverse to the longitudinal axis of said rods, said plates being insulated from each other and from inner and outer conductors, of a pair of electron discharge devices each having a cathode, an anode and a control electrode, means for connecting said cathodes together, a connection from the control electrode of one of said devices to one of said plates, a capacitive connection from the anode of said one device to that rod of the inner conductor immediately adjacent said one plate, a connection from the control electrode of said other device to the other of said plates, and a capacitive connection from the anode of said last device to the other rod of the inner conductor, a resistor connected between the anodes of said devices, and a conu nection from a point intermediate the ends of said resistor to a signal modulator circuit.

3. The combination with an oscillation generator system comprising a pair of oscillators having associated therewith a tuned high frequency circuit comprising concentric inner and outer conductors, said inner conductor comprising a pair of spaced rods arranged in the same straight line and having remote ends connected to said outer conductor, the adjacent ends of said rods being so spaced as to provide a capacitor, and a pair of parallel conducting plates placed between the adjacent ends of said rods with their planes transverse to the longitudinal axis of said rods, said plates being insulated from each other and from said inner and outer conductors, of a pair of electron discharge devices each having a cathode, an anode and a control electrode, means for connecting said cathodes together, a connection from the control electrode of one of said devices to one of said plates, a capacitive connection from the anode of said one device to that rod of the inner conductor immediately adjacent said one plate, a connection from the control electrode of said other device to the other of said plates, and a capacitive for connecting said cathodes together, a connection from the control electrode of one of said devices to one of said plates, a capacitive connection from the anode of said one device to that rod of the inner conductor immediately adjacent said one plate, a connection from the control electrode of said other device to the other of said plates, and a capacitive connection from the anode of said last device to the other rod of the inner conductor, a resistor connected between the anodes of said devices, and a connection from a point intermediate the ends of said resistor to a signal modu- .lator circuit.

5. The combination with an oscillation generator system comprising a pair of oscillators having associated therewith a tuned high frequency circuit comprising concentric inner and outer conductors, said inner conductor comprising a pair of spaced rods having remote ends connected to said outer conductor, the adjacent ends of said rods being so spaced as to provide a capacitor, and a pair of conducting plates placed between the adjacent ends of said rods with their planes substantially transverse to the longitudinal axis of said rods, said plates being insulated from each other and from said inner and outer conductors, of a pair of electron discharge devices each having a cathode, an anode and a control electrode, means for connecting said cathodes together, a connection from the control'electrode of one of l said devices to one of said plates, a capacitive connection from the anode of said one device to that rod of the inner conductor immediately adjacent said one plate, a connection from the control electrode of said other device to the other of said plates, and a capacitive connection from the anode of said last device to the other rod of the inner conductor, a resistor connected between the anodes of said devices, a connection from the midpoint of said resistor to a signal modulator circuit, and means for grounding said midpoint from a radio frequency standpoint.

6. The combination with an oscillation generator system comprising a pair of oscillators having associated therewith a tuned high frequency circuit comprising concentric inner and outer conductors, said inner conductor comprising a. pair of spaced rods having remote ends connected to said outer conductor, the adjacent ends of said rods being so spaced as to provide a capacitor, and a pair of conducting plates placed between the adjacent ends of said rods with their planes substantially transverse to the longitudinal axis of said rods, said plates being insulated .from eac1` other and from said inner and outer conductors, each of said oscillators including an electron discharge device having anode and control electrodes, the anode and control electrode of each oscillator being connected to points of .opposite instantaneous polarity in said tuned circuit, of a pair of electron discharge devices each having a cathode, an anode and a control electrode, means for connecting said cathodes together. a connection from the control electrode of one of said last devices to one of said plates, a capacitive connection from the anode of said one device to that rod of the inner conductor immediately adjacent said one plate, a connection from the control electrode of the other ci said last devices to the other of said plates, and a capacitive connection from the anode of said last device to the other rod of the inner conductor, an impedance connected between the anodes of said devices, and a connection from a point intermediate the ends of said impedance to a signal modulator circuit.

.7. The combination with an oscillation generator system having'associated therewith an oscillatory circuit for controlling the frequency thereincluding an impedance connected between the anodes of saiddevices and a connection from a point on said impedance to a signal modulator.

8. The combination with an oscillation generator system having associated therewith an oscillator'y circuit for controlling the frequency therey of, of an angular velocity modulator circuit for said oscillatory circuit, said modulator circuit being in the form of a pair of electron discharge devices having their anodes coupled to diiierent points of opposite instantaneous polarity on said oscillatory circuit, and means for v varying the conductivity of said pair of eIectron discharge f devices in accordance with signal modulations,

-said means including an impedance connected between the anodes of said devices and a connecotf, of an auxiliary feedback circuit for said oscil- 25 latory circuit, lsaid feedback circuit comprising a v tion from a point on said impedance to asignal modulator.

NILS E. LINDENBLAD. 

